I'll take a whack at a few of those for you in the hope that you will be curious enough to want to learn more, and thus become on of us tube addicts!
As originally designed, each channel of the Foreplay consisted of two amplification stages: The first stage is a Voltage Amplifier, which takes the input signal and increases its amplitude or Voltage. The Voltage Amplifier feeds the amplified signal to the second stage, a Cathode Follower. The purpose of this stage is to provide a low impedance output signal. Impedance is a complex subject, but suffice it to say that lower impedance is desirable for the output of the preamp because it has more oomph to drive the interconnects leading to the input of your power amp.
The nine pins on each of the tubes are numbered according to custom, with the wider spacing between Pin One and Pin Nine. If you have trouble searching up one yourself, write back and I will attempt to link you to a diagram from a specification sheet for the 12AU7 tube in your preamp. It is readily available on line, I'm just being lazy at the moment!
The 12AU7 actually contains two triodes in its glass envelope, each consisting of a Cathode, an Anode (often referred to as a Plate), and a Control Grid to modulate the current flow between the Cathode and Plate. That accounts for six of the nine pins on the 12AU7, with the other three pins being used for the Heaters used to heat the Cathodes.
What Paul was explaining was that a previous owner added some parts to allow your Foreplay to output its signal from two places in the circuit. One output comes directly after the Voltage Amplifier stage, and while its output impedance is relatively high, some prefer a single stage preamp and are willing to accept the lack of drive (using shorter interconnects and a power amp with a high input impedance helps to mitigate the issues) in order to achieve the added clarity that less circuitry in the path of the signal may provide.
The second output in each channel would be from the Cathode Follower, and would essentially follow the original design. In this way, you have a choice and can audition for yourself which arrangement sounds best to you in your set-up, by simply switching the interconnects from one output jack to the other.
Now, the input impedance of a SEX amp is about 100,000 Ohms, so you should get sound either way. Also keep in mind, though, that the SEX amp doesn't really require a preamplifier at all. It can easily be driven to full output with a great many sources directly, so another experiment would be to connect a source directly to the SEX for a listen, thus eliminating BOTH stages of the Foreplay!
So, there's a taste. If you want more, you've come to the right website, IMO, because there are many, many knowledgeable tube enthusiasts here that are happy to discuss the hobby, and you don't have to be one of them to get answers to your questions.
